1. Field of the Invention
This invention relates to a method and an apparatus for taking pictures which are suited for use in video cameras such as high-definition television cameras.
2. Description of the Related Art
There is an HDTV (high-definition television) camera including a solid-state imaging element array having a matrix of 1920 photosensor pixels in a horizontal direction and 1080 photosensor pixels in a vertical direction. To output signals from all the photosensor pixels of the imaging element array in a 1-frame interval ( 1/30 second), it is necessary to drive the imaging element array at a frequency equal to 74 MHz or higher.
As the number of photosensor pixels constituting an imaging element array increases, a necessary frequency of drive of all the photosensor pixels in a 1-frame interval is higher. As the necessary drive frequency is higher, the rate of electric power consumed by a signal processing circuit following the imaging element array and a clock circuit for the drive of the imaging element array increases and also the number of gates in the signal processing circuit increases. Accordingly, it is desirable to provide an apparatus capable of outputting a high-definition picture signal while driving an imaging element array at a relatively low frequency.
Japanese patent application publication number 2004-180240 discloses first and second imaging apparatuses. The first imaging apparatus includes an imaging element array having a matrix of photosensor cells arranged at a high density. The photosensor cells are separated into groups each of neighboring ones. During low-resolution scanning mode of operation, the cell groups are driven to generate low-resolution video data representing a 1-frame picture extending over the whole of the imaging element array. In this case, signals outputted from the photosensor cells in each group are averaged to form a corresponding segment of the low-resolution video data. During high-resolution scanning mode of operation, only ones selected among the photosensor cells which extend in a partial area within the imaging element array are driven to generate high-resolution video data representing a partial-frame picture. The low-resolution scanning mode of operation and the high-resolution scanning mode of operation are sequentially implemented in every 1-frame interval. The generated low-resolution video data and the generated high-resolution vide data are sequentially outputted at higher than a video rate. For every frame, the generated low-resolution video data is processed. The result of the processing of the generated low-resolution video data is used in deciding the place of the partial area relative to the imaging element array for the next frame. Both an output line for a low-resolution video data segment and an output line for a high-resolution video data segment extend from each photosensor cell in the imaging element array.
The second imaging apparatus in Japanese application 2004-180240 is a modification of the first one. In the second imaging apparatus, only a single output line extends from each photosensor cell in an imaging element array. During low-resolution scanning mode of operation, only photosensor cells in equally-spaced selected rows and equally-spaced selected columns of the imaging element array are driven to generate low-resolution video data representing a 1-frame picture substantially extending over the whole of the imaging element array.
The first and second imaging apparatuses in Japanese application 2004-180240 provide only two different fixed picture resolutions.